When you open the fuel cap in hot weather, is there a big vacuum built up in the tank? If so, that means the air vent is clogged. I have just recently had this experience, but have not traced the vent lines yet.

Just last weekend, my car lost power on the highway and died as if out of fuel, but it only had about 430 miles on the tank of fuel. I did notice the vacuum build up in the tank when I opened the cap, but I put my spare fuel (1 gal. of veggie) in the tank, hand primed and went on. When I fueled up, I could put only 18.5 gal. of diesel in the tank.

__________________
1984 300SD 326,997 miles and counting . . . No wait, my odometer is still dead